1. Field of the Invention
The invention relates to the processing of sampled digitilized signals for providing a discrete cosine transform (DCT).
2. Description of the Prior Art
For a long time fast discrete transforms have been used for the time or spatial compression of data to be transmitted or to be stored. Simple transforms have more especially been used, such as the Walsh-Hadamard transform which has the advantage of requiring only simple circuits but on the other hand only provides a low compression rate.
The need is now felt for fast transforms allowing high compression rates to be reached but however only requiring circuits of acceptable complexity and able to operate in real time.
The use has more particularly been proposed of the DCT, in particular for videotext systems, because it appreciably increases the compression rate. But, even for small length transforms, it is difficult to construct integrated circuits able to operate in real time at the sampling frequencies required, even when the latest algorithms proposed are used, which reduce the complexity of the calculation. In practice, sampling frequencies of 10 MHz can be barely reached for transforms of a length of eight.
A device is also known (document U.S. Pat. No. 4,385,363) for calculating the DCT of a signal. This device uses elementary circuits providing the sum and difference of two inputs. But the device has a pipelined construction with several stages each of which includes adders and multipliers. It implements the Chen and Fralick algorithm and this conception leads to complex architecture.